Implantable drug infusion devices are used to provide patients with a constant and long term dosage or infusion of a drug or any other therapeutic agent. Such devices may be categorized as being active or passive.
Active drug or programmable infusion devices feature a pump or a metering system to deliver the drug into the patient's system. An example of such an active drug infusion device currently available is the Medtronic SynchroMed programmable pump. Such pumps typically include a drug reservoir, a peristaltic pump to pump out the drug from the reservoir, and a catheter port to transport the pumped out drug from the reservoir via the pump to a patient's anatomy. Such devices also typically include a battery to power the pump as well as an electronic module to control the flow rate of the pump. The Medtronic SynchroMed pump further includes an antenna to permit the remote programming of the pump.
Passive drug infusion devices, in contrast, do not feature a pump, but rather rely upon a pressurized drug reservoir to deliver the drug. Thus such devices tend to be both smaller as well as cheaper as compared to active devices. An example of such a device includes the Medtronic IsoMed™. This device delivers the drug into the patient through the force provided by a pressurized reservoir. In particular, this reservoir is pressurized with a drug to between 20–40 psi through a syringe capable of delivering the fluid between 35–55 psi.
Regardless of whether the device is an active or passive drug infusion device, the overriding concern for all drug infusion devices is to ensure patient safety. This includes insuring, among many other things, that only the exact intended amount of drug is delivered to the patient. Thus, one drawback to active devices which feature pumps that are not normally closed, such as those disclosed in U.S. Pat. Nos. 5,277,556; 5,224,843 and 5,219,278 is that in the vent the device malfunctions or changes occur in the fluid pathway, then more drug than intended may reach the patient. Similar risks are inherent in passive devices which, should the flow regulator fail or the pressure reservoir be over pressurized, may lead to more drug than intended to reach the patient.
Yet another problem concerning prior art implantable drug or beneficial agent medical devices is the amount of electrical power which they consume. Implantable medical devices are usually powered by a single primary, non-rechargeable battery. Excessive power consumption in an implantable medical device is highly undesirable because the only remedy for low state of charge in the battery of such a device is battery replacement or device replacement (which generally requires explantation of the device).
Thus there exists a need for an implantable drug infusion or delivery system which features a means of prolonging battery life and maintaining an acceptable state of charge therein.